Scots != Gaelic
Scots = either a dialect of English, or a Germanic language very closely related to English (depending on your politics). Also known as Lallans or Doric. What Rabbie Burns wrote in. Can generally be read by an English speaker with some time, effort, and the help of a decent glossary.
Scottish English = English as it is spoken in Scotland: some different words (taken from Scots) and turns of phrase (e.g., things "go on fire" not "catch fire"), but in written form presents no problems to a speaker of Standard English; when spoken, however, it's a different matter.
Gaelic = Celtic language closely related to (and formerly mutually intelligible with) Irish.